A group of former World Bank officials on Wednesday endorsed Africa's candidate to lead the Bank, Nigerian Finance Minister Ngozi Okonjo-Iweala.

In an open letter, 39 former managers and economists called on the Bank's executive board to make their decision on merit, when the board considers more than one candidate for the job for the first time.

"We believe that Mrs Okonjo-Iweala has outstanding qualifications across the full range of relevant criteria," they said.

Okonjo-Iweala, a former World Bank managing director, and Jose Antonio Ocampo, a former finance minister of Colombia, are competing with the US nominee Jim Yong Kim, a public health expert and president of Dartmouth College.

Under a tacit agreement, the US picks the World Bank president, always an American, and Europe puts a European at the helm of the International Monetary Fund, the Bank's sister institution.

The World Bank plans to select the successor to outgoing president Robert Zoellick by April 20, the start of its spring meetings with the IMF.

Writing in their personal capacity ahead of the candidate interviews next week, the ex-Bank officials said "we care too much for the institution and for its historic development mission not to speak up."

The letter was signed by a number of Europeans, including Francois Bourguignon, who was the development lender's chief economist in 2003-2007, as well as Barbara Kafka, an American who served over 33 years at the Bank in a range of posts.

Tunisia's central bank chief, Mustapha Nabli, a former head of the Bank's Middle East and North Africa region, also signed. His country has not endorsed a candidate.

Okonjo-Iweala "would bring the combination of her experience as finance and foreign minister of a large and complex African country with her wide experience of working at all levels of the Bank's hierarchy in different parts of the world, from agricultural economist to managing director," the letter read.

While the other two candidates also have strong qualifications, "she would be the outstanding World Bank president the times call for," it added.

Ocampo, an economics professor at Columbia University in New York who has written extensively on growth and development issues, is being endorsed by a global cross-section of economists.

An Internet petition supporting his candidacy, on economist Kevin Gallagher's TripleCrisis blog, had more than a hundred signatures from academic economists, former central bank chiefs and the heads of international agencies.

In a Financial Times opinion article published online, Ocampo defended his candidacy, citing his "36 years in development."

Ocampo outlined his vision for "a brave new World Bank," which he said could fight poverty "not only with economic growth and job creation, but also by addressing inequalities that have risen in most countries in recent decades, and by eradicating all forms of gender inequality."

The favored US candidate for the post, Kim, is supported by Canada, Japan and South Korea, where he was born.